Circuits that produce a pulse based upon a notch detected in an AC power signal have been described in the prior art. For example, U.S. Pat. No. 6,580,230 teaches a dimmer circuit with a phase detector which monitors the phase angle difference between voltage and current applied to a gaseous discharge device. Changes in the phase angle between the power voltage and current are used to produce a pulse that is in turn used to transfer information to a plurality of ballasts that use the received voltages as a power supply. The circuit of the '230 patent uses a fixed reference point, such as a zero crossing, to determine a phase angle difference between the voltage and current. Using this method of data transmission, the width of a pulse created based upon the zero crossings varies dramatically with changes in the input voltage. Thus, when a pulse is created based upon the detected phase difference between the line voltage and current, the width of the pulse will vary for a low input line voltage, such as 108 V, and a high input line voltage, such as 305 V. This is important due to the fact that many modern electronic devices are designed to be used with either a 120 V or 277 V input line voltage that has a tolerance of plus or minus 10%. The primary disadvantage of using the prior art zero crossing detection circuit is that when the generated pulse width changes due to changes in the input voltage, detection of the pulses produced becomes more difficult and the output of the detection circuit is difficult to interpret. This makes the transmission and reception of data complicated and unreliable.
Therefore, what is needed is a receiver circuit for detecting data bits represented by notches in an input power voltage that generates a constant output pulse width irrespective of the input line voltage.